The present invention relates to a device for supplying liquids, particularly fuel.
One such device is disclosed in DE 196 38 332 A1. This device has a geared supply pump, the pump having a pair of meshed, rotatable gear wheels, by which one gear wheel is rotatably driven by a drive shaft. In the pump chamber, an inlet on the suction side of the geared supply pump opens for the supply liquid and on the pressure side, an outlet for the supplied liquid is provided. The drive shaft is mechanically driven by an internal combustion engine, for example, to which the device supplies the fuel. Upon starting of the internal combustion engine, the geared supply pump drives the device with only a low speed of rotation so that only a small fuel volume is supplied, which under the circumstances, does not make possible a guaranteed starting of the internal combustion engine. Especially with a higher fuel temperature and a lower rotational speed of the internal combustion engine, for example, as a result of an insufficient voltage in an electrical voltage source used for starting the engine, the supply pump supplies an insufficient amount of fuel. The geared supply pump could be modified in this regard so that it supplies a greater amount of fuel. However, under other operating conditions, the supplied fuel volume would be too large and would have to be needlessly regulated.
In contrast with the above-described device, the present invention provides the advantage that with low pressure on the pressure side, the first geared supply pump switches on a second geared supply pump by means of a coupling arrangement, and thereby, the supplied amount of liquid is increased. When the pressure on the pressure side of the first geared supply pump is sufficiently high, and by means of the first geared supply pump, a sufficiently high amount of liquid is supplied, the second geared supply pump is no longer driven by means of the coupling arrangement.
The present invention also makes possible a suctioning of liquid by means of both geared supply pumps through a common inlet. In addition, with the present invention, a flowing-out of the liquid supplied through both geared supply pumps is made possible by means of a common outlet, whereby, by means of the check or relief valve, a flowing-away of the fuel is prevented when the second geared supply pump is switched on. The present invention also provides that the flowing away of a portion of the liquid volume supplied by the first geared supply pump is dependent on pressure on the pressure side, whereby the supplied volume can be limited. In addition, a preferred embodiment of the coupling arrangement is contemplated and will be described in greater detail below.